New Orleans (Tier VII)
Surface detectability increased from 11.82 km to 12.42 km, and in-smoke firing detectability increased from 6.62 km to 7.05 km.
Main gun reload time reduced from 15 seconds to 13 seconds; in-tech-tree main gun upgrade was removed.
I am not sure if she retains radar or not.
(New Orleans also loses her access to Slot 5 due to downtier)

Baltimore (Tier VIII)
Armored extremities reduced to 25 mm.
Main gun reload time reduced from 15 seconds to 13 seconds; in-tech-tree main gun upgrade was removed.
She retains a sigma of 2.05.
(also loses access to heal and slot 6 due to downtier, but she keeps the Super-Heavy Shell, looked on GM3D to confirm, it's included)

Buffalo (Tier IX)
Armored extremities increased to 27 mm.
Main gun reload time reduced from 15 seconds to 13 seconds.
Buffalo has the highest alpha strike of any T9 cruiser at a total of 60,000 max AP damage on a 12 gun broadside. However, it is currently unknown whether she keeps the torpedoes she had back a long time ago, chances are she doesn't.